The invention relates to illumination systems, and in particular to illumination systems that include optical channels for distributing light.
The proficiency with which lamps produce and deliver light into a building is described by the product of two terms, luminous efficacy and luminous efficiency. The luminous efficacy (or simply efficacy) of a source is an efficiency at which a lamp converts electrical energy into visible light, and is expressed in lumens per watt. The luminous efficiency (or simply efficiency) of a fixture is the percentage of light that escapes the fixture in relation to the amount of light that is generated inside of it by the lamp, and may be affected by fixture design and the accumulation of dust and dirt on luminare, lamp, and room surfaces.
Systems for collecting sunlight and distributing it within a building have been proposed and some such systems have been built. These systems generally include a solar collector and an optical path for directing received light to areas within the building. They may also include a cold mirror or the like for diverting the infrared portion of the solar spectrum to make electricity or heat. The use of an optical path for the distribution of artificially generated light has also been proposed. Products exist that include a lamp and a light guide, permitting exclusion of the lamp from environments with explosion or fire hazardous conditions, environments sensitive to radio and magnetic interference, cooled spaces, and locations (e.g., above swimming pools) where relamping is difficult. A need for a highly efficient light piping system exists.
Selectively reflective coatings have been provided on tungsten lamps to reflect radiated energy in the near-infrared back to the filament of the lamp.
Artificial illumination, however, generally remains an inefficient process, typically converting much less than 50% of its input energy into visible light.